Communication networks based on Long Term Evolution (LTE) are all deployed in licensed carriers. Along with the development of LTE, some enterprises have put forward ‘a subject of proposals on the deployment of LTE in unlicensed carriers’, for example, America's Qualcomm believes that as data services increase sharply, licensed carriers cannot bear the huge traffic brought by the rapid service increase in the future. It is considered to deploy LTE on unlicensed carriers to share the traffic in licensed carriers so as to eliminate the traffic pressure brought by the increase of services. Meanwhile, an unlicensed carrier has the following features: on one hand, the unlicensed carrier is free or low-cost because it is not needed to buy, in other words, the cost of carrier resource is zero; on the other hand, the access requirement of the unlicensed carrier is low because apart from individuals and enterprises, devices of manufactures can participate in deploying unlicensed carrier; besides, because the unlicensed carrier is sharable, in a case where a plurality of different systems work in an unlicensed carrier or different operators of the same system work in an unlicensed carrier, some resource sharing methods can be taken into consideration to improve carrier efficiency.
In conclusion, although the deployment of LTE in unlicensed carrier has obvious advantages, the deployment confronts problems, for example, multiple access technologies are required, (the multiple access technologies cross different communication standards, resulting in difficult cooperation and various network topologies), and many wireless access stations are needed (a great number of users, difficult cooperation and high cost on centralized management). Due to the use of various wireless access technologies, various wireless systems exist in an unlicensed carrier, making it difficult to coordinate the wireless systems and leading to a serious interference among the wireless systems. Therefore, the regulation on an unlicensed carrier should be supported in a case where LTE is deployed in the unlicensed carrier, and it is required in many countries that a listening-before-talking mechanism should be supported in the deployment of a system in an unlicensed carrier. Through the listening-before-talking mechanism, the interference is avoided which is caused by neighboring systems when the neighboring systems use unlicensed carriers at the same time. A contention withdrawal mechanism is further introduced, that is, the interference resulted from the synchronous use of an unlicensed carrier by neighboring transmission nodes of the same system is avoided between neighboring system stations (generally, neighboring transmission nodes of the same system).
At present, the deployment of LTE in an unlicensed carrier (that is, a Licensed Assisted Access (LAA) system) is being researched, and it is considered by many enterprises that the downlink of an LAA system will adopt a contention withdrawal mechanism to compete for a right for using an unlicensed carrier. However, no proper LAA systems have been determined, especially, a contention withdrawal mechanism and procedure suitable for an LAA system have not been designed yet in the conventional art after the fairness for the contention mechanism of a Wireless Local Area Network (WLAN) system is taken into consideration.
No effective solutions have been proposed to address the problem that a contention withdrawal mechanism and procedure suitable for an LAA system are not provided in the conventional art.